A FIFO is a first in, first out, temporary data storage device. It is useful for sharing data between real-time tasks and user-level applications. A FIFO is often used to connect a non-real-time machine interface to a real-time application (e.g. to log messages to disk files).
A FIFO in its simplest form is a queue of raw storage units. Typically, fixed-size data structures are written to a FIFO, so that a device reading the data is not burdened with message boundaries. The queued nature of a FIFO makes it best suited for ordered streams of data such as: messages or error diagnostics where the message can include a timestamp for later analysis; data logs for performance metrics; and configuration information at system start-up, among others.
A FIFO, on a higher level, is an array of registers that stores data. The data is often read from and written to devices with different clock domains. The conventional way to transfer data in different clock domains is to synchronize the read and write clocks in the control logic. However, when the read control signal and the write control signal are synchronized, penalties are incurred in the form of delays. The read and write blocks, which are sharing the data, are often clocked at different frequencies, which introduces unwanted delays in the transfer of data between the blocks.
The delays are normally incurred in the control circuit. The control circuit involves the FIFO write control signal and FIFO read control signal. Based on the read and write control signals, a status signal is produced, such as non-limiting examples of FIFO empty or FIFO full. An overflow signal is another status signal, but it is more like an error condition. A status signal can be used to control the transfer of data.
A delay is incurred when the read control signal is synchronized with the write control signal. The read signal is processed some number of clocks later than the write signal. Since the write signal fills the FIFO faster than the read signal can empty it, some delay is incurred.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.